PROFESSOR POWELL ON THE REPULSIVE POWER OF HEAT. 48^ 



This is still more conspicuous when the rings are formed in a thin plate of water 

 between the lenses. The effect is here even greater than in air, and, as we may pre- 

 sume, independent of radiation *=. 



We may then conclude, upon the whole, that the repulsive effect depends upon the 

 amoiint of heat communicated to thc^second surface by whatever means. 



Also, according to what was shown at first, viz. that heat cannot overcome capillary 

 attraction, it follows that in the case of an interposed liquid the heat must be sup- 

 posed to act by exciting repulsion directly between the two surfaces themselves, 

 through the fluid, and not by weakening the attraction of the liquid for either of 

 them. 



* This variation of my experiment was first tried by Professor Foubes of Edinburgh, on receiving an account 

 which I communicated to him of my experiments in January 1834. 



